1 //===-- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils ----*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This family of functions perform manipulations on basic blocks, and 11 // instructions contained within basic blocks. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 16 #define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 17 18 // FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock 19 20 #include "llvm/ADT/ArrayRef.h" 21 #include "llvm/IR/BasicBlock.h" 22 #include "llvm/IR/CFG.h" 23 #include "llvm/IR/InstrTypes.h" 24 #include <cassert> 25 26 namespace llvm { 27 28 class MemoryDependenceResults; 29 class DominatorTree; 30 class LoopInfo; 31 class Instruction; 32 class MDNode; 33 class ReturnInst; 34 class TargetLibraryInfo; 35 36 /// Delete the specified block, which must have no predecessors. 37 void DeleteDeadBlock(BasicBlock *BB); 38 39 /// We know that BB has one predecessor. If there are any single-entry PHI nodes 40 /// in it, fold them away. This handles the case when all entries to the PHI 41 /// nodes in a block are guaranteed equal, such as when the block has exactly 42 /// one predecessor. 43 void FoldSingleEntryPHINodes(BasicBlock *BB, 44 MemoryDependenceResults *MemDep = nullptr); 45 46 /// Examine each PHI in the given block and delete it if it is dead. Also 47 /// recursively delete any operands that become dead as a result. This includes 48 /// tracing the def-use list from the PHI to see if it is ultimately unused or 49 /// if it reaches an unused cycle. Return true if any PHIs were deleted. 50 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 51 52 /// Attempts to merge a block into its predecessor, if possible. The return 53 /// value indicates success or failure. 54 bool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT = nullptr, 55 LoopInfo *LI = nullptr, 56 MemoryDependenceResults *MemDep = nullptr); 57 58 /// Replace all uses of an instruction (specified by BI) with a value, then 59 /// remove and delete the original instruction. 60 void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 61 BasicBlock::iterator &BI, Value *V); 62 63 /// Replace the instruction specified by BI with the instruction specified by I. 64 /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The 65 /// original instruction is deleted and BI is updated to point to the new 66 /// instruction. 67 void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 68 BasicBlock::iterator &BI, Instruction *I); 69 70 /// Replace the instruction specified by From with the instruction specified by 71 /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. 72 void ReplaceInstWithInst(Instruction *From, Instruction *To); 73 74 /// Option class for critical edge splitting. 75 /// 76 /// This provides a builder interface for overriding the default options used 77 /// during critical edge splitting. 78 struct CriticalEdgeSplittingOptions { 79 DominatorTree *DT; 80 LoopInfo *LI; 81 bool MergeIdenticalEdges = false; 82 bool DontDeleteUselessPHIs = false; 83 bool PreserveLCSSA = false; 84 85 CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr, 86 LoopInfo *LI = nullptr) 87 : DT(DT), LI(LI) {} 88 89 CriticalEdgeSplittingOptions &setMergeIdenticalEdges() { 90 MergeIdenticalEdges = true; 91 return *this; 92 } 93 94 CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() { 95 DontDeleteUselessPHIs = true; 96 return *this; 97 } 98 99 CriticalEdgeSplittingOptions &setPreserveLCSSA() { 100 PreserveLCSSA = true; 101 return *this; 102 } 103 }; 104 105 /// If this edge is a critical edge, insert a new node to split the critical 106 /// edge. This will update the analyses passed in through the option struct. 107 /// This returns the new block if the edge was split, null otherwise. 108 /// 109 /// If MergeIdenticalEdges in the options struct is true (not the default), 110 /// *all* edges from TI to the specified successor will be merged into the same 111 /// critical edge block. This is most commonly interesting with switch 112 /// instructions, which may have many edges to any one destination. This 113 /// ensures that all edges to that dest go to one block instead of each going 114 /// to a different block, but isn't the standard definition of a "critical 115 /// edge". 116 /// 117 /// It is invalid to call this function on a critical edge that starts at an 118 /// IndirectBrInst. Splitting these edges will almost always create an invalid 119 /// program because the address of the new block won't be the one that is jumped 120 /// to. 121 /// 122 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 123 const CriticalEdgeSplittingOptions &Options = 124 CriticalEdgeSplittingOptions()); 125 126 inline BasicBlock * 127 SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 128 const CriticalEdgeSplittingOptions &Options = 129 CriticalEdgeSplittingOptions()) { 130 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), 131 Options); 132 } 133 134 /// If the edge from *PI to BB is not critical, return false. Otherwise, split 135 /// all edges between the two blocks and return true. This updates all of the 136 /// same analyses as the other SplitCriticalEdge function. If P is specified, it 137 /// updates the analyses described above. 138 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 139 const CriticalEdgeSplittingOptions &Options = 140 CriticalEdgeSplittingOptions()) { 141 bool MadeChange = false; 142 TerminatorInst *TI = (*PI)->getTerminator(); 143 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 144 if (TI->getSuccessor(i) == Succ) 145 MadeChange |= !!SplitCriticalEdge(TI, i, Options); 146 return MadeChange; 147 } 148 149 /// If an edge from Src to Dst is critical, split the edge and return true, 150 /// otherwise return false. This method requires that there be an edge between 151 /// the two blocks. It updates the analyses passed in the options struct 152 inline BasicBlock * 153 SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 154 const CriticalEdgeSplittingOptions &Options = 155 CriticalEdgeSplittingOptions()) { 156 TerminatorInst *TI = Src->getTerminator(); 157 unsigned i = 0; 158 while (true) { 159 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 160 if (TI->getSuccessor(i) == Dst) 161 return SplitCriticalEdge(TI, i, Options); 162 ++i; 163 } 164 } 165 166 /// Loop over all of the edges in the CFG, breaking critical edges as they are 167 /// found. Returns the number of broken edges. 168 unsigned SplitAllCriticalEdges(Function &F, 169 const CriticalEdgeSplittingOptions &Options = 170 CriticalEdgeSplittingOptions()); 171 172 /// Split the edge connecting specified block. 173 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, 174 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 175 176 /// Split the specified block at the specified instruction - everything before 177 /// SplitPt stays in Old and everything starting with SplitPt moves to a new 178 /// block. The two blocks are joined by an unconditional branch and the loop 179 /// info is updated. 180 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, 181 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 182 183 /// This method introduces at least one new basic block into the function and 184 /// moves some of the predecessors of BB to be predecessors of the new block. 185 /// The new predecessors are indicated by the Preds array. The new block is 186 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors 187 /// from Preds are now pointing. 188 /// 189 /// If BB is a landingpad block then additional basicblock might be introduced. 190 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more 191 /// details on this case. 192 /// 193 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 194 /// no other analyses. In particular, it does not preserve LoopSimplify 195 /// (because it's complicated to handle the case where one of the edges being 196 /// split is an exit of a loop with other exits). 197 /// 198 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 199 const char *Suffix, 200 DominatorTree *DT = nullptr, 201 LoopInfo *LI = nullptr, 202 bool PreserveLCSSA = false); 203 204 /// This method transforms the landing pad, OrigBB, by introducing two new basic 205 /// blocks into the function. One of those new basic blocks gets the 206 /// predecessors listed in Preds. The other basic block gets the remaining 207 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both 208 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and 209 /// 'Suffix2', and are returned in the NewBBs vector. 210 /// 211 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 212 /// no other analyses. In particular, it does not preserve LoopSimplify 213 /// (because it's complicated to handle the case where one of the edges being 214 /// split is an exit of a loop with other exits). 215 /// 216 void SplitLandingPadPredecessors(BasicBlock *OrigBB, 217 ArrayRef<BasicBlock *> Preds, 218 const char *Suffix, const char *Suffix2, 219 SmallVectorImpl<BasicBlock *> &NewBBs, 220 DominatorTree *DT = nullptr, 221 LoopInfo *LI = nullptr, 222 bool PreserveLCSSA = false); 223 224 /// This method duplicates the specified return instruction into a predecessor 225 /// which ends in an unconditional branch. If the return instruction returns a 226 /// value defined by a PHI, propagate the right value into the return. It 227 /// returns the new return instruction in the predecessor. 228 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 229 BasicBlock *Pred); 230 231 /// Split the containing block at the specified instruction - everything before 232 /// SplitBefore stays in the old basic block, and the rest of the instructions 233 /// in the BB are moved to a new block. The two blocks are connected by a 234 /// conditional branch (with value of Cmp being the condition). 235 /// Before: 236 /// Head 237 /// SplitBefore 238 /// Tail 239 /// After: 240 /// Head 241 /// if (Cond) 242 /// ThenBlock 243 /// SplitBefore 244 /// Tail 245 /// 246 /// If Unreachable is true, then ThenBlock ends with 247 /// UnreachableInst, otherwise it branches to Tail. 248 /// Returns the NewBasicBlock's terminator. 249 /// 250 /// Updates DT and LI if given. 251 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 252 bool Unreachable, 253 MDNode *BranchWeights = nullptr, 254 DominatorTree *DT = nullptr, 255 LoopInfo *LI = nullptr); 256 257 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 258 /// but also creates the ElseBlock. 259 /// Before: 260 /// Head 261 /// SplitBefore 262 /// Tail 263 /// After: 264 /// Head 265 /// if (Cond) 266 /// ThenBlock 267 /// else 268 /// ElseBlock 269 /// SplitBefore 270 /// Tail 271 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 272 TerminatorInst **ThenTerm, 273 TerminatorInst **ElseTerm, 274 MDNode *BranchWeights = nullptr); 275 276 /// Check whether BB is the merge point of a if-region. 277 /// If so, return the boolean condition that determines which entry into 278 /// BB will be taken. Also, return by references the block that will be 279 /// entered from if the condition is true, and the block that will be 280 /// entered if the condition is false. 281 /// 282 /// This does no checking to see if the true/false blocks have large or unsavory 283 /// instructions in them. 284 Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 285 BasicBlock *&IfFalse); 286 287 } // end namespace llvm 288 289 #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 290
